(a) Field of the Invention
The present invention relates to an electro-optical display device and, more particularly, to an electro-optical display device, such as a liquid crystal display (LCD device), for displaying an image by using an electro-optical effect. The present invention also relates to an image projection unit having such an electro-optical display device.
(b) Description of the Related Art
Some electro-optical display devices such as a liquid crystal display (LCD) device are used as image display units of a direct view type in a variety of equipment, or light valves of image projection units. The electro-optical display device generally includes an electro-optical substance layer such as a liquid crystal (LC) layer and a pair of substrates sandwiching therebetween the electro-optical substance layer. One of the substrates, a TFT substrate, mounts thereon an array of pixels each including a pixel electrode and a switching device such as a TFT (thin film transistor) for driving the pixel electrode, whereas the other of the substrates, a counter substrate, mounts thereon a counter electrode substantially over the entire area.
In an electro-optical display device, light incident onto the counter substrate is modulated by the electro-optical substance and then emitted through the TFT substrate. The TFT substrate mounts thereon interconnections including a plurality of data lines extending in the column direction, a plurality scanning lines extending in the row direction, and a plurality of capacitive lines in association with the respective pixels. These interconnections are disposed within the gap between the opening areas of adjacent two pixels. A shield film pattern, such as a black matrix, covers and thus shields these interconnections, and also shields against leakage light deviated by ill-oriented molecules of the electro-optical substance.
If the electro-optical display device is used as a light valve of an image projection unit, the light from the light source is incident as a parallel ray onto the counter substrate in the direction of the normal line thereof. The incident light passes through the electro-optical substance, to be projected onto a screen by means of an optical system of the image projection unit for display of an image.
In the TFT substrate, a transparent substrate body is generally made of a material including silicon dioxide as a main component thereof. Silicon is used as the semiconductor active layers for the TFTs whereas silicon dioxide is used as the insulating films for the TFTs. The storage capacitor used for increasing the charge-storage capability of the pixel includes a capacitor insulation film made of a high-dielectric-constant material such as silicon nitride. A protective film made of silicon nitride, for example, overlies the TFTs and interconnections for protecting the TFTs and interconnections made of a metal or alloy against water.
Each pixel of an LCD device, for example, includes an opening area divided from the opening area of another pixel and passing therethrough incident light, and a peripheral area shielded by the shield film and encircling the opening area. The peripheral area, or shielded area, encompasses the interconnections and TFT. For improving the brightness of the LCD device, it is desired to increase the open area ratio, which is defined by the ratio of the opening area to the total area of the pixel. In general, the LCD device has an opening area ratio of around 50% at most.
In the LCD device, a slope is generally formed in the vicinity of the TFT due to the layered structure of gate lines and other interconnections. This slope refracts the light incident onto the substrate in the direction normal to the substrate surface. Thus, even the light passed by the shield film pattern within the opening area may be incident onto the TFT or interconnections covered by the shield film pattern. This fact causes the effective open area ratio to be lower than the nominal open area ratio, thereby reducing the brightness of the LCD device. In addition, the light, if it is incident onto the channel of the TFT, generates a leakage current flowing through the TFT during the OFF state thereof, thereby degrading the contrast ratio of the LCD device.
For solving the above problems, it is proposed in Patent Publication JP-A-2001-133810 that a silicon nitride film having a higher refractive index do not protrude from the edge of the shield film toward the opening area. It is also proposed in Patent Publications JP-A-2002-91339 and -2001-4988 that the layered structure has a specific refractive index profile in the slope area. The specific refractive index profile is such that the refractive index decreases along the travelling direction of the light, for refracting the light passing in the vicinity of the edge of the shield film pattern toward the opening area of the pixel, to thereby increase the effective open area ratio.
The proposals by the above publications may suppress the light incident onto the interconnections and TFTs, to improve the transmittance of the LCD device and suppress the leakage current.
It is also proposed in Patent Publication JP-A-2002-131776 that a SiN film having a higher refractive index be removed in the opening area of the pixel to increase the transmittance of the opening area. It is also proposed in Patent Publication JP-A-2001-66587 that a bottom shield film pattern formed between the TFT and the transparent substrate body have a width substantially equal to the width of the corresponding data line, thereby reducing the amount of returned light, which once passes the LCD device and returns thereto by the optical system of the image projection unit to thereby degrade the image quality thereof.